In a typical radio communications network, also known as wireless communications network, wireless terminals, also known as mobile stations, mobile terminals and/or user equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks. The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” or “eNodeB”. A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not collocated. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole mobile network is also broadcasted in the cell. One base station may have one or more cells. A cell may be downlink and/or uplink cell. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.
A Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some versions of the RAN as e.g. in UMTS, several base stations may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS) have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the radio base station nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of a RNC are distributed between the radio base stations nodes, e.g. eNodeBs in LTE, and the core network. As such, the Radio Access Network (RAN) of an EPS has an essentially “flat” architecture comprising radio base station nodes without reporting to RNCs.
A terminal is supposed to monitor control signals continuously to be able to send and receive actual data. In LTE, these control signals are sent on a Physical Downlink Control Channel (PDCCH). But monitoring PDCCH becomes a waste of radio resources and battery power particularly in the case when no uplink (UL) or downlink (DL) transmission is scheduled for longer periods. Discontinuous Reception (DRX) is one possible solution to avoid this situation, which means that a terminal stays asleep and wakes up only at particular interval of times to monitor PDCCH for any data transfer.
In High Speed (HS) networks, DRX works together with Channel Switching (CS). An HS channel, such as Dedicated Channel (DCH), is power and radio resource consuming, so when a user does not have an active burst, such as an IP packet exchange, it is switched down to a less power consuming channel, such as Forward Access Channel (FACH) or Paging Channel (PCH). Channel switching works on a few second timescale, while DRX works on a few ten milliseconds timescale.
A DRX Cycle is illustrated in FIG. 1, wherein a terminal monitors the PDCCH, and the DRC cycle specifies the periodic repetition of the On Duration followed by a possible period of inactivity. A DRX Inactivity Timer specifies the number of consecutive PDCCH-subframe(s) after successfully decoding a PDCCH indicating an initial UL or DL user data transmission for this terminal. DRX Retransmission Timer specifies the maximum number of consecutive PDCCH-subframe(s) for as soon as a DL retransmission is expected by the terminal. DRX Short Cycle Timer specifies the number of consecutive subframe(s) the terminal shall follow a short DRX cycle after the DRX Inactivity Timer has expired. On Duration Timer specifies the number of consecutive PDCCH-subframe(s) at the beginning of a DRX Cycle. In DRX operation the terminal may be configured by Radio resource Control (RRC) with a DRX functionality that allows it to monitor the PDCCH discontinuously. DRX operation is based on a Long DRX cycle, a DRX Inactivity Timer, a HARQ RTT Timer, a DRX Retransmission Timer and optionally a Short DRX Cycle and a DRX Short Cycle Timer.
When a DRX cycle is configured, the Active Time includes the time while:                the On Duration Timer or the DRX Inactivity Timer or a DRX Retransmission Timer or the Contention Resolution Timer is running; or        a Scheduling Request is pending; or        an uplink grant for a pending HARQ retransmission can occur; or        a PDCCH indicating a new transmission addressed to a Cell Radio Network Temporary Identifier (C-RNTI) or Temporary C-RNTI of the terminal has not been received after successful reception of a Random Access Response.        
When DRX is configured, the terminal shall for each subframe:                If the Short DRX Cycle is used and [(SFN*10)+subframe number] modulo (Short DRX Cycle)=DRX Start Offset; wherein SFN means System Frame Number or        if the Long DRX Cycle is used and [(SFN*10)+subframe number] modulo (Long DRX Cycle)=DRX Start Offset:        start the On Duration Timer.        if a HARQ RTT Timer expires in this subframe and the data in the soft buffer of the corresponding Hybrid Automatic Repeat Request (HARQ) process was not successfully decoded:        start the DRX Retransmission Timer for the corresponding HARQ process.        if a DRX Command MAC control element is received:        stop the On Duration Timer;        stop the DRX Inactivity Timer.        if the DRX Inactivity Timer expires or a DRX Command MAC control element is received in this subframe:        if the short DRX cycle is configured:                    start or restart the DRX Short Cycle Timer;            use the Short DRX Cycle.                        else:                    use the Long DRX cycle.                        if the DRX Short Cycle Timer expires in this subframe:        use the long DRX cycle.        during the Active Time, for a PDCCH-subframe except if the subframe is required for uplink transmission for half-duplex FDD UE operation and except if the subframe is part of a configured measurement gap:        monitor the PDCCH;        if the PDCCH indicates a DL transmission or if a DL assignment has been configured for this subframe:                    start the HARQ Round Trip Time (RTT) Timer for the corresponding HARQ process;            stop the DRX Retransmission Timer for the corresponding HARQ process.                        if the PDCCH indicates a new transmission (DL or UL):                    start or restart the DRX Inactivity Timer.                        
DRX in LTE and HSPA is used to reduce the battery consumption of the terminal when there are short periods with no data transfer for the given user by temporarily switching off the radio. This is a tradeoff between delay and battery lifetime. During DRX sleep the terminal is unable to send or receive any packets, in this way DRX will increase delay while increasing battery lifetime, and there is a problem how to optimize the performance of the wireless communications network experienced by a user and still save battery power.